Future Forest Production and Net Carbon Sinks under Optimal C:N Balance

Environmental change affects forests directly by changing physiological process rates, but the consequent changes in resource acquisition may lead to structural and functional acclimations that obscure the long-term relationship between environmental drivers and forest function. Based on an adaptive balance between structure and function, evolutionary optimisation may provide a feasible tool for analysing such indirect effects of environmental change on forests. This study applies OptiPipe, a model of optimal co-allocation of forest carbon (C) and nitrogen (N), to prediction of potential productivity and C balance of Finnish forests under climate change. OptiPipe is embedded in a transparent modular system including: PreLes, a canopy C exchange model; Yasso, a soil C model; and expert assumptions about the impacts of weather on N availability at different growth sites. National Forest Inventory data and gridded weather data (10 x 10 km2) are utilised. The uncertainties of the projections are analysed relative to inputs and parameters. The results quantify the changes in growth and carbon stocks, which are either smaller or larger than those in photosynthetic capacity, depending on the C:N balance of the site. The results emphasize the need to obtain more reliable information and data about nitrogen processes, but also demonstrate the potential for the optimality approach for regional applications.